Well, only if you think the IRA/Sinn Fein should set UK foreign policy. We could have implemented an (EU-requested) north/south border in Ireland. Or not implemented one at all.
The signatories to the GFA include the US as well - if you want to rip up the GFA to install a hard border you have to own the second order effects of that.
Or decide that Brexit was never going to work the way those who peddled it said it would.
